code: def make_bintree(levels):
      """Make a symmetrical binary tree with @levels"""
      G = nx.DiGraph()
      root = "0"
      G.add_node(root)
      add_children(G, root, levels, 2)
      return G
  
file_path: ipyparallel/examples/dagdeps.py
imports: from random import randint
  import networkx
  import ipyparallel
label_desc: Use image node_id 4 for calling a global function with example usage: make_bintree(levels) and returns: G